Thermodynamic study on inclusion complex formation of riboflavin with hydroxypropyl-β-cyclodextrin in water

The inclusion complex formation of riboflavin (RF) with hydroxypropyl-beta-cyclodextrin (HP-beta-CD) in water was investigated by H-1 NMR, UV-vis spectroscopy, and solubility methods. A 1:1 stoichiometry and thermodynamic parameters of complex formation (K, Delta(c) G (0), Delta(c) H (0), and Delta(c) S (0)) were determined. Complexation was characterized by negative enthalpy and entropy changes due to prevalence of van der Waals interactions and hydrogen bonding between polar groups of the solutes. A partial insertion of RF into macrocyclic cavity was revealed on the basis of H-1 NMR data and molecular mechanics calculation. Location of benzene ring of RF molecule inside the hydrophobic cavity of HP-beta-CD results in an increase of aqueous solubility of the former.